Stabilizing a smoke shell with an interior plastic liner



Dec. 23, 1969 R. I. WESSELLS STABILIZIEG A SMOKE SHELL WITH AN INTERIORPLASTIC LINER PRIOR ART Filed Oct. 23, 1967 INVENTOR. Russell Wessel/sBY 7 1 W United States Patent 3,485,171 STABILIZING A SMUKE SHELL WITHAN INTERIOR PLASTIC LINER Russell I. Wessells, Baltimore, Md., assignorto the United States of America as represented by the Secretary of theArmy Filed Oct. 23, I967, Ser. No. 677,467 lint. Cl. F421: 13/44 US. Cl.102--56 Claims ABSTRACT OF THE DTSCLGSURE The invention relates tostabilizing means and method for producing said means for variousmunitions utilizing a filled curable thermosetting resin as the saidmeans forming a contiguous coating on the internal radial longitudinalwall of the projectiles cavity forming a hollow substantiallycylindrical area which is substantially the central axis of theprojectile.

DEDICATORY CLAUSE The invention described herein may be manufactured,used and licensed by or for the Government for governmental purposeswithout the payment to me of any royalty thereon.

This invention relates to a munition and has for an object to produceone of great stability during trajectory with smoke screening means andat the same time in which the total weight of the munition has notchanged substantially.

The object of the invention is carried forward by utilizing an internalliner of synthetic material to aid in the stabilization of the munition.

Various methods in the past have been investigated in order to bringabout optimal projectile stabilization. The previous methods forstabilizing means include internal bafiles, vanes or bellows all ofwhich presented many problems in fabrication of the munition.

In the US. Patent No. 3,282,714 to Wessells, FIGURE 1, illustrates theinternal fin stabilizing a white phosphorus shell. The shell body 1 witha pair of rifiing band 3, main hollow body 8, buster casing 5 comprisingan extruded or fastened to said casing a plurality of 3-12 radial andlongitudinally extending straight fins or irnpellers 7, and said hollowbody is filled with white phos phorus 9. The fins serve the purpose ofpreventing the free longitudinal movement or oscillation of the liquidwhite phosphorus that is the fins swirl the liquid white phosphorus inflight so that the void is reduced to a thin vortex on an axis ofrotation of the shell, and the fins force the white phosphorus to actsubstantially the same as a solid substance.

The solving of the intricate problem of projectile stabilization hasperplexed the engineers for many years. With the recent changeover tothe thin-walled projectile, additional inquiry had to be made forstabilization since there is now a larger volume containing the warfareagent; this is so in view that the external configuration of the overallthin-walled projectile is identical to the projectile prior to thechangeover to thin-walled munition.

FIGURE 1 is a longitudinal view of the prior art shell with internalfins.

FIGURE 2 is a longitudinal view of a shell illustrating the syntheticliner of my invention.

FIGURE 3 is a longitudinal view of a smoke generating projectileembodying the synthetic liner of this invention.

The ability to obtain the optimal stability of a munition containingwhite phosphorus is greater as compared with a high explosive fill forthe reasons which follow. It is ice required that all munitions beballistically stable over the temperature range from F. to F. The highexplosive warfare agent is a solid at room temperature and remains asolid over the aforesaid temperature range. White phosphorus, to thecontrary, becomes a liquid at about 112 F., and as a result changes froma solid to liquid during the firing cycle. It is this change of state tothe liquid phase which brings about the stability problem. A projectileor shell utilizing white phosphorus requires a void space in the area ofthe nose section to compensate for the increase in volume as a result ofthe phase change. The prior art use of baflies, vanes or bellowsinterfere with the formation of the void space and thereby adding to theproblem of in-flight stability. The position of the said void spacecreates not only problems during the firing cycle, but also the shift ofthe void space when the shell is in a horizontal position as experiencedunder combat conditions. This shift in position of the said void spaceoccurs when the ambient temperature is sufficient to cause the whitephosphorus to melt and then solidify upon cooling. The void space is nowon the side wall of the shell and therefore is asymmetrical to the axisof rotation of the munition. With the asymmetrical void space, the highrevolutions per minute imparted to the projectile during the firingcycle brings about instability in the form of a wobble or tumble. Thisgreatly effects the calculated trajectory and causes the shell to fallin an undesired impact area and may injure friendly troops.

An investigation was instituted to bring about the requiredstabilization of a thin-wall projectile utilizing white phosphorus asthe warfare agent. During the course of my studies, the concept emergedof utilizing an internal liner of thermosetting resins such as expoxies,ureaformaldehyde, phenolics, alkyds and combinations thereof forstabilization. It will be noted in the FIGURES 13 the cavity of theprojectile is not cylindrical since the thickness and/or the internalconfiguration of the shells Wall varies along its longitudinaldimension. By reshaping the internal configuration of the shell, theprinciple involved is to construct the outer diameter of the shapedpayload of the white phosphorus, for example, close to the axis ofrotation of the projectile. As a result, the liquefied white phosphorusformed during the firing cycle can very quickly obtain substantially thesame spin rate or angular velocity as that of the projectile and therebyeliminate forces that the liquid phosphorus may set up within themunition causing yaw or tumble during its trajectory.

Another unexpected result is that the liner acts as a heat shield andaids in substantially reducing the effect of the ambient temperatures ina tropic area where hitherto brought about the asymmetric shift of thevoid space. This effect of ambient temperature is very common in the useof tank-mounted guns where the munition is carried in the tank where thetemperature is about the melting point of white phosphor-us.

A further unexpected result is that upon the fragmentation of theprojectile the liner acting as a heat sink will absorb a portion of theheat of explosion. and as a consequence the white phosphorus burns moreslowly and thereby giving a longer duration for screening effect.Moreover, the liner is also consumed during the burning of the whitephosphorus and thus adding to the density of the smoke cloud.

As a result of the synthetic liner, it is now feasible to modify allshell cavities to take a shaped payload which is substantiallycylindrical in figuration without the added expense of metalfabrication. The liner concept is not limited to munitions utilizingwhite phosphorus as the payload but to other warfare agents that arefluid or 3 become fluid during the firing cycle. The type munition shownin FIGURES 2-3 is representative of the 152 millimeter short projectile;this invention is equally applicable to 105, 107, 155 millimeterartillery shells, mortars, and rocket projectiles.

In FIGURE 2, numeral 1 is the shell body and the infusible syntheticliner 2 forming a coating on the intemal radial longitudinal wall of thehollow body 8. The reshaped cavity of the shell is substantiallycylindrical in configuration. FIGURE 3 is the longitudinal cross sectionof a projectile embodying the synthetic liner of this invention. A fuze4, booster 6, and ogive 10 are provided at the forward end of the shellbody 1. The fuze is responsive to impact although a time or proximityfuze may be employed; The'mairi hollow body Sis "of steel 'or malle ablecast iron adopted to be fragmented upon detonation of the burster casing5 and thereby disseminating the Warfare agent 9. The burster casing 5 isforce-fitted within the axially positioned fill 9.

The synthetic resins employed in preparing the liner in accordance withthe present invention are curable filled thermosetting resin such as RenRP 3262 (Ren Plastics, Inc.), Dural 400 (Dural Materials Corporation),Devcon C or F (Devcon Corporation), or Pleuco 2000 (Plastics EngineeringCompany). The filler may be various powdered metals such as aluminum ormagnesium varying in proportions from about 20% to 65% by weight of thethermosetting resin.

The above named curable thermosetting resins have the followingcharacteristics as thermal coefiicient of expansion about 3.0 1O- to 3.810 (in./in./ F.), heat distortion about 145 to 185 F., tensile strengthULT- p.s.i. about 5600 to 7600, modulus of elasticity in flexure p.s.i.about 1.1 l to 1.4 10 fiexural strength ULT- p.s.i. about 8800 to 9300,compressive strength ULT-p.s.i. about 14,000 to 15,600, hardness aboutM55 to M88, specific gravity about 1.70 to 1.81, pot life about 10 to 45minutes, mixing ratio about 1 to 10 parts by weight of hardner or curingagent to about 1 to 100 parts by weight of the resin. The specificgravity value of the resin is critical since this number is to besubstantially the same as the payload.

Generally, the curing cycle or pot life efiecting the blended polymericresin to remain usable is determined by the type of curing agent and thetime to accomplish the desired hardening of the resin. Aliphatic primaryor secondary amines and many of the tertiary amines begin the process ofcuring the resin at room temperature since the heat of the reaction mayrise to approximately. 100 F. or higher. If desired, an external heatingsource can be utilized in shortening the curing time. I have found itadvantageous for the curing operation to proceed under as mildconditions that production will tolerate in order to minimize the numberof defective shells caused by too rapida curing cycle.

The following is an example illustrating the preparation of the filledcurable thermosetting resin and the method of forming the internalliner.

Example 1 The filled curable thermosetting setting resin is flowablehaving the reacting ratio by weight of about 10/100 curing agent to saidresin respectively, mixed viscosity about 60,000 cps., pot life (1 pt.)35 minutes, specific gravity (cured) about 1.72, density 6.2 10- lbs./cu. in., coefficient of linear thermal expansion about 3.l 10

in./in./ F., hardness Shore D about 75, heat distortion about 164 E,compressive strength ULT-p.s.i. about 13,200 p.s.i., and about 20-65% byweight of aluminum based on the weight of the thermosetting resin. Themixing 7 of the curing agent and said resin can be performed in anysuitable container with stirring from about 1 to 10 minutes until themixture assumes a creamy texture.

The method of forming the internal linear is carried out on aconventional lathe except that no provision is made for shaping themetal portion of the shell. The prepared flowable thermosetting resinfrom about 28 lbs., depending upon size of the projectile, is accuratelyWeighed or measured and placed in the cavity of the shell which isimmediately positioned along its longitudinal axis with the base of theshell attached to the rotating head of lathe being capable of turningbetween 150-600 revolutions per minute. The spinning operation variesfrom 20- minutes which is sufiicient for curing and coating the internalradial longitudinal walls of the shell forming a hard and infusibleliner which has a hollow substantially cylindrical core. There are nofinishing operations required upon the liner'or shell, and the'munition'or projectile is now ready to be processed in the conventionalmanner to receive the payload material.

I claim:

1. An artillery shell comprising an externally shaped body with aninternal elongated shaped cavity having an opening in the nose end ofsaid cavity and a cured thermosetting resin being contiguous with theentire internal radial longitudinal surface of said cavity forming ahollow substantially cylindrical area being substantially the centralaxis of said shell, said cylindrical area being filled with a payload ofwhite phosphorus.

2. A shell according to claim 1, in which the specific gravity value ofthe said thermosetting resin and said payload is substantially the same.

3. A smoke disseminating projectile comprising:

(a) an externally shaped body with an internally elongated shaped cavityhaving an opening in the nose end of said cavity adapted to receive aburster casing (b) a burster casing mounted within the said shapedcavity and in sealing relationship with said opening, extending apredetermined axial distance within the said cavity and adapted toreceive a burster charge (1) said burster charge casing comprising afuze means sealed at its forward end being adjacent to the said opening(0) a cured thermosetting resin is contiguous with the entire internalradial longitudinal surface of the said cavity forming a hollowsubstantially cylindrical area being substantially the central axis ofthe externally shaped body ((1) a liquefiable payload axially positionedbetween the inner surface of the formed said cylindrical area and theexterior surface of said burster casing.

4. A projectile according to claim 3 in which the said payload is Whitephosphorus. 1

5. A projectile according to claim 3, in which the specific gravityvalue of the said resin and said payload is substantially the same.

References Cited UNITED STATES PATENTS 2,195,429 4/ 1940 Shaler 102562,532,323 12/1950 Miller 102-90 2,589,129 3/1952 Ponder et al. 102--63,013,495 12/1961 Stevenson et a1. l0266 3,103,888 9/1963 Rosenthal102-66 3,292,543 12/ 1966 Tisch l02--66 1,605,574 11/1926 Stewartll7-l0l FOREIGN PATENTS 978,435 12/1964 Great Britain. 1,341,656 9/1963France.

BENJAMIN A. BORCHELT, Primary Examiner JAMES FOX, Assistant Examiner US.Cl. X-lR. 10266

